Lighting for Seedlings-when to change over?

Hi everyone,

I've started my first indoor grow in a closet and would like some of the more seasoned experts here to tell me what they think of my set-up and offer any advice they might think useful.

First the specifications:

A mylar lined closet, dimensions 1.8 x 1.05 x .5 metres (.945m3) or,
5.90 x 3.50 x 1.6 feet (33 cubic feet)

Lighting-one 400 watt HPS, two 20 watt CFLS, brand Philips, unsure of spectrum or lumen output)

Ventilation-Exhaust, passive intake with 150mm(6 inch) fan, rated 250 m3/hour (unsure of CFM conversion) fitted in ceiling and intake vent, 100cm2 on opposite side. Also, one small oscillating fan.

I have four plants, germinated from 18th of March and in small pots (soil medium with perlite), for the last ten days now on an 18/6 cycle. Each is about 6cm (2 inches) tall, all with second set of true leaves and third set already forming. I have brought them on under the two CFLs, one bulb over two plants placed close together with the distance between the top of the plants and the bulb at about 10cm (4 inches). My first question is, when should I change over to the HPS light and what distance should I keep between the light and the plants? Also, will I need my exhaust system on at this stage to keep the heat down or will distance suffice?

At what stage should I start feeding the plants? I have BioBizz nutrients, one for vegging and two for flowering?

My third question is about the oscillating fan. Where is the best place to place it, at what height in relation to the plants, and at what side of the closet? All going well, things will get a bit crowded in there and I was wondering should I turn the fan so the air current is rebounded off the wall or have it blow directly onto the plants?

I'm sure I'll have other questions as things progress but right now these are my main concerns. So far I'm happy with the way the plants are developing. They are feminised Grapefruit variety, bought here in a grow shop in Dublin, Ireland-any idea what they're like and how best to care for them?

I'm sure you've answered these types of questions hundreds of times before-I've done some research already and read similar posts-but I suppose it's best to hear what actually is best practise for your own individual set-up, so thanks for your help.

Place the fan at the back blowing the hot air out.

Flourescents: proximimty
400w HPS: 1 foot
600w HPS: 1.5 foot
1000w HPS: 2 foot

Thanks for your answer Mogie, I've been keeping the 400 Hps a foot above the plants and they're thriving. In fact I'm just about to go into flower cycle and my main concern now is that the plants are over crowded. They are just about a foot tall, 40 days old and very bushy. They're already pressing against the walls of the closet and some leaves and stems are getting flattened. I was thinking of taking one out and keeping it as a mother to give the other three more space. Would you recommend this or is it ok it they're all fairly tightly packed together? How do I care for a mother, I mean how many watts does she need and should I just water her or give her nutrients as well?

the ginger man said:

I've been keeping the 400 Hps a foot above the plants and they're thriving. In fact I'm just about to go into flower cycle and my main concern now is that the plants are over crowded. They are just about a foot tall, 40 days old and very bushy.

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Hiya Gingerman

First thing, a foot? Plants don't need that much light in vegetative growth (1/4 of the light requirement of flowering) and in my opinion a foot above the plant tops is too low for vegetative growth - there's no need to have it down that low, you're frying the tops of your plants with IR heat at that distance.

Secondly, regarding your first post, your passive intake seems too small compared to the size of the exhaust fan. As a general rule of thumb you want about 1.5 times the size of the intake fan as a passive intake. So the square area of a 150mm fan is 7.5 squared x 3.14 = 56.25 x 3.14 = 176 sq cm x 50% = 176 + 88 = 264 sq cm passive intake.

the ginger man said:

I was thinking of taking one out and keeping it as a mother to give the other three more space. Would you recommend this or is it ok it they're all fairly tightly packed together? How do I care for a mother, I mean how many watts does she need and should I just water her or give her nutrients as well?

Click to expand...

Do you have the space and resources to keep a mother in Veg while you flower the others? If so go for it. And yes of course you need to feed the mother, try giving her some Biobizz Fish Mix 2-3mil per L of water and see how she likes it, you can also apply fish mix as a foliar feed if you prefer.

Babygro,

Thanks for your informative reply. I've kept the lamp a foot above the plants because that seems to be the general advice given out here and elsewhere and, so far at least, the plants seem to be doing well with no signs of heat damage or stress. I have the oscillating fan blowing across at the level of the plants which probably cools them down a bit too. My temperature is a stable 25 celsius inside the closet.

As for the intake vent, I bought it and it came with a fly-screen, a tight grid of small squares to keep insects from getting in, and I suppose the 100 cm2 referred to the area of holes or the effective intake size because I've just measured it again and it's actual dimensions are 20cm x 20 cm. Well, I subsequently removed the fly screen and that has effectively double active vent size so I should be within the guidelines you mentioned. Thanks!

How about the crowded issue, will four plants in a tight area be fruitful or will I ultimately improve yield by giving them more space. I'm not sure about going with the mother plant yet, I've been looking for an old tea-chest or similar sized box to keep them in but it's hard hard thing to find these days. I still have a few days before change over to flowering.

Maybe you could help me with another issue. I need to attach a carbon filter, thing is it won't fit in directly on top of my fan so I'll have to get a bend, close to 45o in there and have the filter lying horizontally. Now I'm just worried that this bend will reduce the extraction rate. What do you think? If it does then I'll just have to take out the fan, cut a new hole in the closet ceiling and put it back in towards the front where the roof doesn't slant down on it-a lot of work and hassle.